can someone explain that one to me? ISO 100-6400. (12800 with Boost)????

There's a little bit of history that might give that some perspective...

Nikon's first DSLR's had a relatively uncomplex method for adjusting ISO, which was simply to adjust the analog gain between the electronic sensor output and the Analog-Digital-Converter (ADC). Twice as much amplification gave twice the ISO. Over the analog amplification range that at least semi-decent results could be obtained, it was listed as ISO. The original Nikon D1 has ISO values of 200, 400, 800 and 1600 corresponding to 2x, 4x, 8x and 16x amplification. The images were pretty good at ISO 200, and much noisier at ISO 400. ISO 800 was usable with care and effort, and ISO 1600 too noisy and with such a low dynamic range that for normal purposes the image were barely useful.

However, Nikon also supplied, above ISO 1600, three more stops of increased sensitivity using digital amplification. Because it was not analog amplification they didn't call it ISO, and referred to these steps as H1, H2, and H3. The higher noise and lower dynamic range restricted these generally to "documentation" purposes.

The same basic method, with higher gain from better analog amplifiers, was continued with following models at least as far as the D3. Hence to begin with the ISO settings (your 100-6400 range) were those provided by analog amplification, while the "boost" setting were seriously degraded settings provided by additional digital amplification.

But technology has advanced, and the difference between ISO and "boost" is no longer based on that distinction. In the most recent models from Nikon it appears that analog gain is only adjusted at the lower part of the ISO range, and everything higher is a digital manipulation. The difference between what is labeled as ISO and what is labeled as "boost" seems to be based soley on Nikon's concept of where the quality is reduced beyond some pre-determined point rather than the means to achieve it.

can someone explain that one to me? ISO 100-6400. (12800 with Boost)????

There's a little bit of history that might give that some perspective...

[snip]

But technology has advanced, and the difference between ISO and "boost" is no longer based on that distinction. In the most recent models from Nikon it appears that analog gain is only adjusted at the lower part of the ISO range, and everything higher is a digital manipulation. The difference between what is labeled as ISO and what is labeled as "boost" seems to be based soley on Nikon's concept of where the quality is reduced beyond some pre-determined point rather than the means to achieve it.

Very nice job explaining this.

Do you know what amplification algorithm Nikon now uses for the different ISO values? Or at what ISO they switch to pure digital boost?

can someone explain that one to me? ISO 100-6400. (12800 with Boost)????

There's a little bit of history that might give that some perspective...

[snip]

But technology has advanced, and the difference between ISO and "boost" is no longer based on that distinction. In the most recent models from Nikon it appears that analog gain is only adjusted at the lower part of the ISO range, and everything higher is a digital manipulation. The difference between what is labeled as ISO and what is labeled as "boost" seems to be based soley on Nikon's concept of where the quality is reduced beyond some pre-determined point rather than the means to achieve it.

Very nice job explaining this.

Do you know what amplification algorithm Nikon now uses for the different ISO values? Or at what ISO they switch to pure digital boost?

There has been quite a bit of speculation, and each new model seems to be slightly different. But in fact only Nikon knows for sure exactly what they are doing, and even with careful measurements and analysis the rest of us are guessing.